The present invention relates to a surface treated polymethylsilsesquioxane powder and, more particularly, to a surface treated polymethylsilsesquioxane powder with excellent water repellency.
It has conventionally been known that a surface treated polymethylsilsesquioxane powder is obtained by hydrolysis and condensation of a three-functional silane such as methyltrichlorosilane. For example, Belgian Pat. No. 572,412 discloses a process for producing solid polymethylsilsesquioxane by hydrolyzing methyltrichloro-silane and water in an atomized state or while adding dropwise methyltrichlorosilane to a large amount of water under stirring. Such a process, however, is disadvantageous in that a comparatively large quantity of byproduct cholorine atoms remains in the polymethylsilsesquioxane powder produced. To solve this problem, Japanese Patent Laid-Open No. 72300/1979 discloses a method of hydrolyzing and condensing methyltrialkoxysilane and/or a partial hydrolyzate thereof in an aqueous solution which contains an alkaline earth metal hydroxide or an alkaline metal carbonate.
Although this method can solve the problem of the residual chlorine atoms, it brings about a new problem that there remains a comparatively large quantity of alkaline earth metal or alkaline metal in the polymethylsilsesquioxane powder produced. As a countermeasure, Japanese Patent Laid-Open No. 13813/1985 discloses a process for producing a polymethylsilsesquioxane powder which solves the above-described problem and has an excellent fluidity by hydrolyzing and condensing methyltrialkoxysilane and/or a partial hydrolyzate thereof in an aqueous solution of ammonia and/or amine, and Japanese Patent Laid-Open No. 103812/1988 discloses a polymethylsilsesquioxane powder having a spherical particle which is approximate to a perfect sphere. Such a polymethylsilsesquioxane powder obtained by a conventional process is useful as an additive for improving the durability and lubricating properties of rubber and plastic and also serves to provide them with repellency.
Rubber, plastic, etc. with a polymethylsilsesquioxane powder produced in a conventional method added thereto do not necessarily have adequate repellency for some uses. This is because a slight quantity of silanol group exists on the surface of a polymethylsilsesquioxane powder produced in a conventional method, which leads to the inadequate repellency.
One of the present inventors has disclosed a technique of providing a perfectly spherical polymethylsilsesquioxane powder with an electrified nature by treating the powder with a compound having at least two functional groups such as an alkoxy group in Japanese Patent Laid-Open No. 101857/1988. Such a polymethylsilsesquioxane powder, however, does not have sufficiently improved water repellency.